Integrating Josephson amplifiers or Josephson mixers into printed circuit boards

ABSTRACT

An aspect includes one or more board layers. A first chip cavity is formed within the one or more board layers, wherein a first Josephson amplifier or Josephson mixer is disposed within the first chip cavity. The first Josephson amplifier or Josephson mixer comprises at least one port, each port connected to at least one connector disposed on at least one of the one or more board layers, wherein at least one of the one or more board layers comprises a circuit trace formed on the at least one of the one or more board layers.

BACKGROUND

The present invention generally relates to superconducting devices. Morespecifically, the present invention is directed to integrating Josephsonamplifiers or Josephson mixers into printed circuit boards.

Superconducting quantum computing is an implementation of a quantumcomputer in superconducting electronic circuits. Quantum computationstudies the application of quantum phenomena for information processingand communication. Various models of quantum computation exist, and themost popular models incorporate the concepts of qubits and quantumgates. A qubit is a generalization of a bit that has two possiblestates, but can be in a quantum superposition of both states. A quantumgate is a generalization of a logic gate, however the quantum gatedescribes the transformation that one or more qubits will experienceafter the gate is applied on them, given their initial state.

The electromagnetic energy associated with the qubit can be stored inso-called Josephson junctions and in the capacitive and inductiveelements that are used to form the qubit. In one example, to read outthe qubit state, a microwave signal is applied to the microwave readoutcavity that couples to the qubit at the cavity frequency. Thetransmitted (or reflected) microwave signal goes through multiplethermal isolation stages and low-noise amplifiers that are required toblock or reduce the noise and improve the signal-to-noise ratio. Themicrowave signal is measured at room temperature. The amplitude and/orphase of the returned/output microwave signal carry information aboutthe qubit state, such as whether the qubit is at the ground or excitedstates or at a superposition of the two states. The microwave signalcarrying the quantum information about the qubit state is usually weakon the order of a few microwave photons. To measure this weak signalwith room temperature electronics, low-noise Josephson amplifiers areusually used as preamplifiers (first amplification stage) at the outputof the quantum system to boost the quantum signal and improve the signalto noise ratio of the output chain. In addition to Josephson amplifiers,certain Josephson microwave components that employ Josephson amplifiersor Josephson mixers such as Josephson circulators, Josephson isolators,and Josephson mixers are expected to play a crucial role in scalablequantum processors and quantum communication.

Josephson parametric amplifiers are high-gain, low-noise amplifiers thatare used in the readout of qubits and the measurement of quantumsystems.

A Josephson ring modulator (JRM) is a nonlinear dispersive element basedon Josephson tunnel junctions that can perform three-wave mixing ofmicrowave signals at the quantum limit. The JRM consists of JosephsonJunctions (JJs). In order to construct a non-degenerate parametricdevice that is the Josephson parametric converter (JPC) (which is oneexample of Josephson parametric amplifiers), which is capable ofamplifying and/or mixing microwave signals (without amplification) atthe quantum limit, the JRM is coupled to two different microwaveresonators.

SUMMARY

Embodiments of the present invention are directed to printed circuitboards. A non-limiting example of the printed circuit board includes oneor more board layers. A first chip cavity is formed within the one ormore board layers, wherein a first Josephson amplifier or Josephsonmixer is disposed within the first chip cavity. The first Josephsonamplifier or Josephson mixer comprises at least one port, each portconnected to at least one connector disposed on at least one of the oneor more board layers, wherein at least one of the one or more boardlayers comprises a circuit trace formed on the at least one of the oneor more board layers.

Embodiments of the present invention are directed to printed circuitboards. A non-limiting example of the printed circuit board includes adielectric substrate. A first chip cavity and a second chip cavity areformed within the dielectric substrate, wherein a first Josephsonamplifier or Josephson mixer is disposed within the first chip cavityand a second Josephson amplifier or Josephson mixer is disposed withinthe second chip cavity. The first chip cavity and the second chip cavitycan be formed utilizing any etching, removal, and/or fabricationtechniques for printed circuit boards or the like known in the art. Eachof the Josephson amplifiers or Josephson mixers comprise at least oneport, each port electronically coupled to at least one connector andeach of the at least one connector is disposed on the dielectricsubstrate.

Embodiments of the present invention are directed to printed circuitboards. A non-limiting example of the printed circuit board includes oneor more board layers. A first chip cavity and a second chip cavity areformed within the one or more board layers, wherein a first Josephsonamplifier or Josephson mixer is disposed within the first chip cavityand a second Josephson amplifier or Josephson mixer is disposed withinthe second chip cavity. A coupler is disposed on at least one of the oneor more board layers, wherein the coupler comprises a first leg and asecond leg and the first leg is electronically coupled to the firstJosephson amplifier or Josephson mixer and the second leg iselectronically coupled to the second Josephson amplifier or Josephsonmixer

Embodiments of the present invention are directed to integratingJosephson amplifiers or Josephson mixers into printed circuit boards. Anon-limiting example of the method of integrating Josephson amplifiersor Josephson mixers into printed circuit boards includes providing oneor more board layers. Forming a first chip cavity within the one or moreboard layers, wherein the first chip cavity is operable to receive aJosephson amplifier or Josephson mixer. A Josephson amplifier orJosephson mixer is disposed into the first chip cavity and at least oneconnector is disposed on at least one of the one or more board layers

Embodiments of the present invention are directed to integratingJosephson amplifiers or Josephson mixers into printed circuit boards. Anon-limiting example of the method for integrating Josephson amplifiersor Josephson mixers into printed circuit boards includes providing adielectric layer. A first chip cavity and a second chip cavity areformed within the dielectric substrate, wherein the first chip cavity isoperable to receive a first Josephson amplifier or Josephson mixer andthe second chip cavity is operable to receive a second Josephsonamplifier or Josephson mixer. The first Josephson amplifier or Josephsonmixer is disposed into the first chip cavity and the second Josephsonamplifier or Josephson mixer is disposed into the second chip cavity. Atleast one connector is disposed on at least one of the one or more boardlayers

Additional technical features and benefits are realized through thetechniques of the present invention. Embodiments and aspects of theinvention are described in detail herein and are considered a part ofthe claimed subject matter. For a better understanding, refer to thedetailed description and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The specifics of the exclusive rights described herein are particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features and advantages ofthe embodiments of the invention are apparent from the followingdetailed description taken in conjunction with the accompanying drawingsin which:

FIG. 1 depicts an example of a Josephson directional amplifier 100without illustrating a 90° hybrid coupler according to embodiments ofthe present invention;

FIG. 2 depicts an example hybrid coupler according to one or moreembodiments of the present invention;

FIG. 3 depicts a top view of a Josephson amplifier or Josephson mixerintegrated within a printed circuit board (PCB) according to one or moreembodiments of the invention;

FIG. 4 depicts bottom view of a Josephson amplifier or Josephson mixerintegrated within a printed circuit board (PCB) according to one or moreembodiments of the invention;

FIG. 5 depicts a buried or internal board layer of the printed circuitboard (PCB) according to one or more embodiments of the presentinvention;

FIG. 6 depicts a top view of two Josephson amplifier or Josephson mixerintegrated within a printed circuit board (PCB) according to one or moreembodiments of the invention;

FIG. 7 depicts a bottom view of two Josephson amplifier or Josephsonmixer integrated within a printed circuit board (PCB) according to oneor more embodiments of the invention; and

FIG. 8 depicts top view of a printed circuit board (PCB) integrated withtwo Josephson amplifiers or Josephson mixers according to one or moreembodiments of the present invention.

The diagrams depicted herein are illustrative. There can be manyvariations to the diagram or the operations described therein withoutdeparting from the spirit of the invention. For instance, the actionscan be performed in a differing order or actions can be added, deletedor modified. Also, the term “coupled” and variations thereof describeshaving a communications path between two elements and does not imply adirect connection between the elements with no interveningelements/connections between them. All of these variations areconsidered a part of the specification.

DETAILED DESCRIPTION

For the sake of brevity, conventional techniques related tosemiconductor and/or superconducting devices and integrated circuit (IC)fabrication may or may not be described in detail herein. Moreover, thevarious tasks and process steps described herein can be incorporatedinto a more comprehensive procedure or process having additional stepsor functionality not described in detail herein. In particular, varioussteps in the manufacture of semiconductor and/or superconducting devicesand semiconductor/superconductor-based ICs are well known and so, in theinterest of brevity, many conventional steps will only be mentionedbriefly herein or will be omitted entirely without providing thewell-known process details.

Turning now to an overview of technologies that are more specificallyrelevant to aspects of the invention, Josephson-based microwave circuitssuch as, for example, directional amplifiers, circulators, isolators,switches, require the integration of multiple Josephson amplifiers orJosephson mixers together. As superconducting quantum processors arescaled up, they are expected to require a large number ofquantum-limited Josephson amplifiers in order to preform high-fidelity,quantum nondemolition (QND) measurements of the qubits states. Packagingthese amplifiers individually in separate packages or separate cryopermmagnetic shield cans is impractical in the long run and is not possiblein large quantum processors.

Turning now to an overview of the aspects of the invention, one or moreembodiments of the invention address the above-described shortcomings ofthe prior art by providing integration of Josephson-based microwavecircuits into a printed circuit board (PCB).

More specifically, the above-described aspects of the invention addressthe shortcomings of the prior art (such as full on-chip integration orcombining discrete components in separate packages) by providingenhanced flexibility, reduced cost, increased modularity, and simplifiedcouplings to normal-metal microwave circuits and components such as, forexample, lumped-element capacitors, lumped-element inductors, andlumped-element resistors. Additionally, the integration scheme enablesthe placement of high-density Josephson amplifiers and/or Josephsonmixers that would be needed in large-scale quantum processors. Usingthis integration scheme, crosstalk between various components can becontrolled, reduced, or mitigated using various microwave techniquessuch as, for example, using vias, using different packages for differentcomponents, and routing signals through different metallic layers.Another two advantages of breaking the device into multiple chipsconnected through a PCB are the (1) elimination of low-frequency, chipmodes associated with large size chips or large metallic packages and(2) to provide better thermalization to the fridge stage.

FIG. 1 depicts an example of two Josephson parametric amplifiers whichwork in reflection, in this case JPCs, integrated with a microwavecomponent, i.e., a 90° hybrid coupler, to form a more sophisticatedJosephson microwave device, which is in this example a Josephsondirectional amplifier 100. FIG. 1 showing the Josephson directionalamplifier does not illustrate the 90° hybrid coupler according toembodiments of the present invention. However, it should be appreciatedthat the hybrid coupler 104 is connected although not shown. Each ofthree-wave-mixing Josephson amplifiers 102_1 and 102_2 includes aJosephson ring modulator (JRM) 1010 which is a nonlinear dispersiveelement based on (4) Josephson tunnel junctions 1006 in an outer ringwhich can perform three-wave mixing of microwave signals at the quantumlimit. Particularly, the JRM 1010 consists of four nominally identicalJosephson junctions arranged in a Wheatstone bridge configuration.

In each of the three-wave-mixing Josephson amplifiers 102_1 and 102_2,one of the microwave resonators is depicted as resonator_a 1002 and theother is resonator_b 1004. The resonators_a 1002 can be referred to asSignal resonators and the resonators_b 1004 can be referred to as Idlerresonators. The resonators 1002 and 1004 are shown as transmission-lineresonators, but the resonators 1002 and 1004 can be implemented aslumped elements, etc. In FIG. 1, the 90° hybrid coupler 104 would beconnected to ports a1_1 and a2_1. For example, FIG. 2 depicts port a1_1from Signal resonator_a 1002 of three-wave-mixing Josephson amplifier102_1 connected to one leg of the 90° hybrid coupler 104 and port a2_1from Signal resonator_a 1002 of three-wave-mixing Josephson amplifier102_2 connected to the opposite leg of the 90° hybrid coupler 104. FIG.2 is only a partial view of the Josephson directional amplifier 100illustrating connection of the resonators 1002 to the hybrid coupler104.

In FIG. 1, the ports b1_2 and b2_1 are electronically coupled. There arevarious ways of feeding the pump signals 1 and 2 to the Josephsonamplifiers 102_1 and 102_2 which have equal amplitudes, the samefrequency f_(p), but have a zero or nonzero phase difference. As oneexample, in FIG. 1 the pumps p1 and p2 can be fed to on-chip flux linesin the form of short-circuited coupled stripline that are capacitivelycoupled to two adjacent nodes of the JRM 1010. Such pump lines can bothsupport microwave tones at the pump frequency and direct current (DC)currents that flux bias the JRMs. A low-pass filter 1012 can be coupledin between the pump port and the flux line 1008 to prevent power leakagefrom the Signal 1002 and Idler 1004 resonators. Another way for fluxbiasing the JRMs is by using external magnetic coils attached to theJosephson amplifiers or Josephson mixers package and/or using a verysmall magnetic material integrated on chip or in the package. Anotherway to feed the pump drives is by using an on-chip 3-port power dividerthat capacitively couples to opposite nodes of the JRM 1010. Further,each resonator_a 1002 and resonator b_1004 has two ends.

FIG. 1 shows that the one end of resonator_a 1002 is capacitivelycoupled to a feedline that connects to one port of the 90° hybrid 104(a1_1 for Josephson amplifier/mixer 102_1 and a2_1 for Josephsonamplifier/mixer 102_2). The other end of resonator_a 1002 is connectedto a feedline that is shorted to ground (a1_2 for Josephsonamplifier/mixer 102_1 and a2_2 for Josephson amplifier/mixer 102_2). Oneend of resonator_b 1004 (b1_2 for Josephson amplifier/mixer 102_1 andb2_1 for Josephson amplifier/mixer 102_2) is capacitively coupled to ashared transmission line between the two resonators_b of the twoJosephson amplifiers/mixers 102_1 and 102_2. The other end ofresonator_b (b1_1 for Josephson amplifier/mixer 102_1 and b2_2 forJosephson amplifier/mixer 102_2) is capacitively coupled to a feedlinethat is terminated by a 50 Ohm load.

In one or more embodiments, each mixer 102_1 and 102_1 is a Josephsonparametric converter. In FIG. 1, the first Josephson parametricconverter 102_1 includes a Signal resonator (e.g., resonator_a 1002)electronically coupled to the Signal port a1 and the second Josephsonparametric converter 102_2 includes another Signal resonator (e.g.,resonator_a 1002) electronically coupled to another Signal port a2. Thefirst Josephson parametric converter 102_1 includes an Idler resonator(e.g., resonator_b 1004) coupled to the Idler port b1 and the secondJosephson parametric converter 102_2 includes another Idler resonator(e.g., resonator_b 1004) coupled to the other Idler port b2. One leg ofa hybrid coupler 104 is electronically coupled to the Signal port a1_1and another leg of the hybrid coupler 104 is electronically coupled tothe other Signal port a2_1. One port of the 90° hybrid 104 that is notdirectly connected to the JPC ports a1_1 and a2_1, forms port 1 of thewhole device. Similarly, another port of the 90° hybrid 104 that is notdirectly connected to either JPC ports a1_1 and a2_1, forms port 2 ofthe whole device. Ports 1 and 2 carry the input and output signals ofthe directional Josephson amplifier. An example of a PCB-integratedJosephson directional amplifier is presented in FIG. 8.

In one or more embodiments, the Josephson amplifiers or Josephson mixersdescribed herein can be integrated in to printed circuit boards (PCBs).

FIG. 3 depicts a top view of a Josephson amplifier or Josephson mixerintegrated within a printed circuit board (PCB) according to one or moreembodiments of the invention. As mentioned herein, electronic componentscan be connected to printed circuit boards (PCBs), also known as printedwiring boards (PWBs). Printed circuit board (PCB) technology generallyinvolves forming conductive traces on an insulating substrate to effectoften complex interconnections between electronic components mounted toor plugged into the PCB. PCBs having conductive traces on both sides ofthe board, as well as multi-layer arrangements of alternating insulatingand conductive layers. Additionally, effecting connections fromlayer-to-layer, within the PCB, can be done through vias. It shouldclearly be understood that, in any of the embodiments describedhereinbelow setting forth PCB substrates, these substrates can be formedof materials other than “traditional” printed circuit board materials.For example, the “PCB” substrate can be formed of one or more layers ofplastic material, such as polyimide, optionally with conductive foillayers sandwiched there between.

Digital electronics and other devices, including analog devices, aremounted on printed circuit boards which are designed to be placed insidean electrical or electronic device or product. Similar to theinterconnections between devices located within a chip, the variouscomponents mounted on a printed circuit board are connected byelectrical pathways, typically metal interconnections known as “traces.”The traces are typically thin lines of deposited conductive material,usually copper. The design and the configuration of the interconnectionsbetween the components on the printed circuit board determines theboard's function. Most printed circuit boards typically contain multipleinter-connected layers. Thus, an entire circuit or “net” may be locatedentirely on the interior layers of a board. As a practical matter, thenets of the board almost always extend to an exterior layer.

The printed circuit board (PCB) 300 includes multiple metallic anddielectric layers as described above. The exterior (top) layer includesfour connectors (302_1, 302_2, 302_3, 302_4) and a top cover 304arranged on the exterior layer. The four connectors (302_1, 302_2,302_3, 302_4) can be any type of connector including but not limited toSMA, SSMA, SMB, SMP, and the like. The four connectors can also behigh-density connectors that connect to high-density traces on the PCB300. The four connectors can be soldered, surface mounted, mechanicallypressed, or the like. The layering and connecting of the various traces,board layers, and components can be performed by any printed circuitboard assembly techniques.

FIG. 4 depicts bottom view of the Josephson amplifier or Josephson mixerintegrated within a printed circuit board (PCB) according to one or moreembodiments of the invention. The exterior (bottom) layer includes abottom cover 414 arranged on the exterior layer. Both the top cover 304and the bottom cover 414 are operable to enclose the Josephson amplifieror Josephson mixer integrated within the printed circuit board 300. Thetop cover 304 and bottom cover 414 can be a high-thermal-conductivitypackage attached to the PCB 300 such as, for example, anoxygen-free-high-conductivity (OFHC) copper and gold.

FIG. 5 depicts a buried or internal board layer of the printed circuitboard according to one or more embodiments. The buried board layer 500includes a cavity 502. The cavity 502 is operable to receive a Josephsonamplifier or Josephson mixer such as the three-wave-mixing amplifiers102_1 or 102_2 described in FIG. 1. The buried board layer 500 includesfour traces 506 each terminating into the cavity 502 and at atermination point 504_1-504_4. The termination points 504_1 to 504_4 canconnect to the connectors 302_1 to 302_4 from FIG. 3. The traces 506 canbe wire bonded to ports a1_1, a2_2, b1_1, and b1_2 of the Josephsonamplifier of 102_1 from FIG. 1. The PCB 300 can include the top layer,bottom layer, and multiple buried board layers (e.g., 500) that areconnected utilizing any PCB fabrication technique. Additionally, thetraces 506 of the buried board layer 500 can be connected to traces ofother buried layers and/or the top and bottom layer utilizing vias. Viasare an electrical connection between layers in a physical electroniccircuit that go through the plane of one or more adjacent layers.

FIG. 6 depicts a top view of two Josephson amplifier or Josephson mixerintegrated within a printed circuit board (PCB) according to one or moreembodiments of the invention. The printed circuit board 600 includesmultiple board layers as described above. The exterior (top) layerincludes four connectors (602_1, 602_2, 602_3, 602_4) and a top cover604 arranged on the exterior layer. The exterior layer of the PCB 600includes traces 606 formed on the exterior layer. Used herein, “traces”can be any electronic transmission line such as, for example,striplines, microstrips, coplanar waveguides, coupled-striplines, andthe like. The traces 606 on the exterior (top) layer can be connected totraces or other elements disposed on other layers of the PCB 600utilizing vias or other transmission means.

FIG. 7 depicts a bottom view of two Josephson amplifier or Josephsonmixer integrated within a printed circuit board (PCB) according to oneor more embodiments of the invention. The exterior (bottom) layerincludes a first chip cavity 702_1 and a second chip cavity 702_2. Thefirst chip cavity 702_1 and second chip cavity 702_2 are sized andconfigured to receive an integrated circuit chip such as, for example, aJosephson amplifier or Josephson mixer. The exterior (bottom) layerincludes multiple traces 706 that connect the first chip cavity 702_1and the second chip cavity 702_2. In addition, the traces 706 canconnect to the traces 606 on the exterior (top) layer utilizing vias.The traces 706 through the vias and traces 606 can connect the Josephsonamplifiers or Josephson mixers to the connectors 602_1 to 602_4. Thetraces 706 can be wire bonded to ports a1_1, a2_2, b1_1, and b1_2 of aJosephson amplifier or Josephson mixer disposed within each of thecavities 702_1 and 702_2. The PCB also 600 includes a bottom cover 704that can be arranged on the exterior (bottom) layer. Both the top cover604 and the bottom cover 704 are operable to enclose the two Josephsonamplifier or Josephson mixer integrated within the printed circuit board600. The top cover 604 and bottom cover 704 can be ahigh-thermal-conductivity package attached to the PCB 600 such as, forexample, an oxygen-free-high-conductivity (OFHC) copper and gold. Thebottom cover 704 includes a cavity 708 that can enclose the twoJosephson amplifiers or Josephson mixers such that the bottom cover 704does not contact any of the traces 706. The top cover 604 provides amounting surface for the two Josephson amplifiers or Josephson mixers.Similar to the bottom cover the top cover 604 does not contact any ofthe traces 606

FIG. 8 depicts top view of a printed circuit board integrated with twoJosephson amplifiers or Josephson mixers according to one or moreembodiments of the present invention. The circuit diagram of thisPCB-integrated Josephson device is shown in FIGS. 1 and 2. The printedcircuit board 800 includes the components of the Josephson amplifier orJosephson mixer 102_1, 102_2, the hybrid coupler 104, Pump 1, Pump 2,and the other various components found in FIGS. 1 and 2. The PCB 800includes six connectors (802_1 to 802_6). The six connectors (802_1 to802_6) can be any type of connector including but not limited to SMA,SSMA, SMB, SMP, and the like. The six connectors can also behigh-density connectors that connect to high-density traces on the PCB800. Each of the six connectors (802_1 to 802_6) are coupled todifferent ports from the Josephson amplifiers or Josephson mixers 102_1and 102_2 and the hybrid coupler 104 of FIGS. 1 and 2. Connector 802_1is coupled to Port 1 of the hybrid coupler 104. Connector 802_2 iscoupled to Port 2 of the hybrid coupler 104. Connector 802_3 is coupledto the input port of Pump 1 of 102_1 and connector 802_4 is coupled toPump 2 of 102_2. Connector 802_5 is coupled to port b1_1 of 102_1 andconnector 802_6 is coupled to port b2_2 of 102_2. The six connectors(802_1 to 802_6) can be coupled to their respective ports utilizing anycombination of traces and vias formed on one or more layers of the PCB800. An internal layer of the PCB 800 includes a hybrid coupler formedon the internal layer and connected to the connectors 802_1 and 802_2utilizing any combination of traces and vias. Additionally, the firstand the second leg of the hybrid coupler 104 (e.g., output ports) can becoupled to the input ports a1_1 and a2_1 of Josephson amplifiers orJosephson mixers 102_1 and 102_2, respectively, utilizing anycombination of traces and vias across one or more layers of the PCB 800.The PCB 800 includes a top cover 804 can mount/enclose the Josephsonamplifiers or Josephson mixers 102_1 and 102_2 integrated within the PCB800. The top cover 804 can be a high-thermal-conductivity packageattached to the PCB 800 such as, for example, anoxygen-free-high-conductivity (OFHC) copper and gold.

In one or more embodiments, the printed circuit boards described hereincan be arranged to form an array (or arrays) of Josephson amplifiers orJosephson mixers that are separate from each other (have their own inputand output connectors) or coupled together to form other Josephsondevices. The array can be in a regular or irregular pattern. The circuitboards can route signals, such as microwave signals, between Josephsonamplifiers or Josephson mixers or other microwave components integratedin the PCB or PCBs including quantum processors. The PCBs include one ormore metallic and/or dielectric layers. The dielectrics can be low-loss,dielectric substrates. The metallic layers can include low-loss, normalmetal or superconducting materials. The connectors described herein canbe surface mount microwave connectors for input/output or high-densitymicrowave connectors. The traces (i.e., transmission lines) in the PCBscan be in the form of microstrip, stripline, coplanar waveguide, andcoupled stripline, for example.

In one or more embodiments of the present invention, the PCBs describedherein can have more than two Josephson amplifiers or Josephson mixersintegrated in the PCB. The Josephson amplifiers or Josephson mixersintegrated in the PCBs can be housed in high-conductivity packagesattached to the PCB. The PCBs with the integrated Josephson amplifiersor Josephson mixers can be utilized to form more sophisticated microwavecircuits needed for scaling up quantum processor such as, for example,quantum-limited amplifiers, circulators, isolators, and switches.

In one or more embodiments, the PCB metallic layers can be any ofcopper, gold, silver, aluminum, and indium, for example. The PCBs canalso be substituted with printed wiring boards, organic substrates, andsimilar substrates that support flip-chip technology, in which the padsof the chip are connected to the substrate through bump bonds or bumpsolder.

Various embodiments of the present invention are described herein withreference to the related drawings. Alternative embodiments can bedevised without departing from the scope of this invention. Althoughvarious connections and positional relationships (e.g., over, below,adjacent, etc.) are set forth between elements in the followingdescription and in the drawings, persons skilled in the art willrecognize that many of the positional relationships described herein areorientation-independent when the described functionality is maintainedeven though the orientation is changed. These connections and/orpositional relationships, unless specified otherwise, can be direct orindirect, and the present invention is not intended to be limiting inthis respect. Accordingly, a coupling of entities can refer to either adirect or an indirect coupling, and a positional relationship betweenentities can be a direct or indirect positional relationship. As anexample of an indirect positional relationship, references in thepresent description to forming layer “A” over layer “B” includesituations in which one or more intermediate layers (e.g., layer “C”) isbetween layer “A” and layer “B” as long as the relevant characteristicsand functionalities of layer “A” and layer “B” are not substantiallychanged by the intermediate layer(s).

The following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” “contains” or “containing,” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, acomposition, a mixture, process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such composition, mixture, process, method, article, or apparatus.

Additionally, the term “exemplary” is used herein to mean “serving as anexample, instance or illustration.” Any embodiment or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The terms “at least one”and “one or more” are understood to include any integer number greaterthan or equal to one, i.e. one, two, three, four, etc. The terms “aplurality” are understood to include any integer number greater than orequal to two, i.e. two, three, four, five, etc. The term “connection”can include an indirect “connection” and a direct “connection.”

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedcan include a particular feature, structure, or characteristic, butevery embodiment may or may not include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

The terms “about,” “substantially,” “approximately,” and variationsthereof, are intended to include the degree of error associated withmeasurement of the particular quantity based upon the equipmentavailable at the time of filing the application. For example, “about”can include a range of ±8% or 5%, or 2% of a given value.

As previously noted herein, for the sake of brevity, conventionaltechniques related to superconducting device and integrated circuit (IC)fabrication may or may not be described in detail herein. By way ofbackground, however, a more general description of the superconductingdevice fabrication processes that can be utilized in implementing one ormore embodiments of the present invention will now be provided. Althoughspecific fabrication operations used in implementing one or moreembodiments of the present invention can be individually known, thedescribed combination of operations and/or resulting structures of thepresent invention are unique. Thus, the unique combination of theoperations described in connection with the fabrication of asemiconductor device according to the present invention utilize avariety of individually known physical and chemical processes performedon a superconducting over a dielectric (e.g., silicon) substrate, someof which are described in the immediately following paragraphs.

In general, the various processes used to form a micro-chip that will bepackaged into an IC fall into general categories, including, filmdeposition, removal/etching, and patterning/lithography. Deposition isany process that grows, coats, or otherwise transfers a material ontothe wafer. Available technologies include physical vapor deposition(PVD), chemical vapor deposition (CVD), electrochemical deposition(ECD), molecular beam epitaxy (MBE) and more recently, atomic layerdeposition (ALD) among others. Removal/etching is any process thatremoves material from the wafer. Examples include etch processes (eitherwet or dry), and chemical-mechanical planarization (CMP), and the like.Films of both conductors (e.g., poly-silicon, aluminum, copper, etc.)and insulators (e.g., various forms of silicon dioxide, silicon nitride,etc.) are used to connect and isolate components. Lithography is theformation of three-dimensional relief images or patterns on thesemiconductor substrate for subsequent transfer of the pattern to thesubstrate. In lithography, the patterns are formed by a light sensitivepolymer called a photo-resist. To build the complex structures of acircuit, lithography and etch pattern transfer steps are repeatedmultiple times. Each pattern being printed on the wafer is aligned tothe previously formed patterns and slowly the conductors, insulators andother regions are built up to form the final device.

The flowchart and block diagrams in the Figures illustrate possibleimplementations of fabrication and/or operation methods according tovarious embodiments of the present invention. Variousfunctions/operations of the method are represented in the flow diagramby blocks. In some alternative implementations, the functions noted inthe blocks can occur out of the order noted in the Figures. For example,two blocks shown in succession can, in fact, be executed substantiallyconcurrently, or the blocks can sometimes be executed in the reverseorder, depending upon the functionality involved.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdescribed herein.

What is claimed is:
 1. A printed circuit board (PCB) comprising: one ormore board layers; and a first chip cavity formed within the one or moreboard layers, wherein a first Josephson amplifier or Josephson mixer isdisposed within the first chip cavity; wherein the first Josephsonamplifier or Josephson mixer comprises at least one port, each portconnected to at least one connector disposed on at least one of the oneor more board layers; wherein at least one of the one or more boardlayers comprises a circuit trace formed on the at least one of the oneor more board layers; a first cover and a second cover; the first coveroperable to mount or enclose the first Josephson amplifier or Josephsonmixer, wherein the first cover is disposed on a first external layer ofthe one or more board layers; and the second cover operable to enclosethe first Josephson amplifier or Josephson mixer, wherein the secondcover is disposed on a second external layer of the one or more boardlayers.
 2. The printed circuit board of claim 1, wherein the first andsecond covers comprise an oxygen-free high conductivity (OFHC) copper.3. The printed circuit board of claim 1, wherein one or more circuittraces are formed on at least one of the one or more board layers. 4.The printed circuit board of claim 3, further comprising: one or morevias connecting the one or more circuit traces formed on the one or moreboard layers.